Rotary piston, positive displacement compressors



March 22, 1966 L. B. SCHIBBYE ETAL 3,241,744

ROTARY PISTON, POSITIVE DISPLACEMENT COMPRESSORS Filed Oct. 1, 1963 5 Sheets-Sheet 2 INVE TOR. ZN? M if 4' March 22, 1966 sc ETAL 3,241,744

ROTARY PISTON, POSITIVE DISPLACEMENT COMPRESSORS Filed 001:. 1, 1963 5 Sheets-Sheet 3 c INVENTOR. BY 49% MM 4. ATTORNEY March 22, L B SCHIBBYE ETAL ROTARY PISTON, POSITIVE DISPLACEMENT COMPRESSORS Filed 001;. 1, 1963 5 Sheets-Sheet 4 III/1% 1 HIV-TH l Z m I INVENTOR.

f z W M A ATTORNEY March 22, 1966 SCHIBBYE L 3,241,744

ROTARY PISTON, POSITIVE DISPLACEMENT COMPRESSORS Filed Oct. 1, 1963 5 Sheets-Sheet 5 IAHIl /l Z t z Ira 55g T511 M BY A. ATTORNEY United States Patent 3,241,744 ROTARY PISTON, POSITIVE DISPLACEMENT (IOMPRESSORS Lauritz Benedictus Schibbye, Saltsjoduvnas, and Hans Robert Nilsson, Ektorp, Sweden, assignors to Svenska Rotor Maskiner Alrtiebolag, Nacka, Sweden, a corporation of Sweden Filed Oct. 1, 1963, Ser. No. 313,118 Claims priority, application Sweden, Sept. 1, 1959, 8,076/59 21 Claims. (Cl. 230-143) This application is a continuation-in-part of our application Serial Number 52,455 filed August 29, 1960, now abandoned, which corresponds to and from which priority is claimed from our Swedish application Serial Number 8076/1959, filed September 1, 1959, and as to all common subject matter relates back for all dates and rights incident to the filing of the aforesaid application.

The present invention relates to rotary piston positive displacement compressors of the kind commonly referred to as screw compressors. Such compressors are characterized generally by the creation of compression chambers formed by the intermeshing action of the lands of two intermeshing helically threaded rotors acting in conjunction with a suitably ported enclosing casing structure providing inlet and discharge ports, the compression chambers decreasing in volume as the rotors revolve between the time of cutofl of the chambers from the inlet port and the time of communication of the chambers with the discharge port, to thereby provide an in-built compression ratio within the compressor. Such compressors further fall into either one of two major cate gories, the earliest developed of which categories is the so-called dry compressor of which the compressor disclosed in Lysholm, U.S. Patent No. 2,243,874 granted June 3, 1941 is a pioneer example. Dry compressors are characterized by the fact that the compression chambers are sealed by means by what is generally referred to as space packing, that is, packing afforded by extremely close clearances which are maintained between the intermeshing rotors through the intermediary of synchronizing or timing gears, and equally close clearances between the peripheries and the end surfaces of the rotors and the enclosing casing structure, established by precision manufacture of these parts. In such compressors there is always leakage from the compression chambers through these small clearance spaces and characteristically such compressors are always operated at relatively very high tip speeds of the circumferences of the rotors in order to reduce to as small a percentage as possible the leakage loss through such clearance spaces and thus provide the highest possible volumetric efiiciency for the device.

The second and more recently developed category of such compressors is the so-called wet or flooded type, in which a liquid, usually oil such as ordinary lubricating oil, is introduced into the compression chambers for the dual purpose of providing a liquid seal for closing the clearance spaces and also for the purpose of cooling the gaseous fluid being compressed directly during the compression phase of the cycle. The compressor disclosed in the Bailey et al., US. Patent No. 3,073,514 granted January 15, 1963 constitutes a pioneer example of this latter category of compressor.

In a dry compressor, as previously noted, it is desirable to operate rotors at the highest practical tip speed and it is also desirable to keep the clearance spaces as small as practically possible in order to reduce the leakage losses. Such high speeds of operation and close clearances produce a relatively high degree of agitation of the fluid passing through the leakage spaces which in turn results in the production of what is generally 3,241,744 Patented Mar. 22, 1966 referred to as ventilation losses and for the purposes of this specification ventilation losses resulting from the agitation of the gaseous fluid involved will be referred to as turbulence losses.

In a wet or flooded compressor, the inherent cooling action of the liquid introduced into the compressor results in lower temperature differentials than in the case of a dry compressor. Consequently the degree of thermal deformation is less and as a result such compressors may ordinarily be safely operated with smaller or closer clearances than in the case of a dry compressor. On the other hand, the film of liquid which is established between the cooperating surfaces of the intermeshing rotor lands and the cooperating surfaces between the rotors and the casing results in ventilation losses due to the presence of the liquid which are substantially higher than the ventilation losses attributable to a gaseous fluid, even though in the case of the wet compressor the tip speeds of the rotors are very much lower than the tip speeds of a comparable dry compressor. This higher ventilation loss is due to the much greater viscosity of a liquid as compared with a gaseous fluid, and for the purposes of this specification the ventilation losses attributable to the liquid will hereinafter be referred to as churning losses.

The present invention relates specifically to compressors of the wet or flooded type, and in one of its aspects has as a principal objective the improvement of the overall efiiciency of the compressor through the reduction of the churning losses created by the presence of the liquid in the compressor. This objective is obtained through the provision of novel improvements in structure hereinafter more fully described as this specification proceeds.

As previously noted, in compressors of the kind under consideration the compression chambers are defined in part by intermeshing portions of the lands of the cooperating rotors and in the normal operation of a wet compressor there is a certain amount of leakage or blow past these intermeshing surfaces of a mixture of gaseous fluid and liquid from the relatively high pressure within a compression chamber to the relatively lower pressure outside that chamber. The liquid content of this mixture blowing from the compression chamber has been heated above inlet temperature by the heat of compression generated in the chamber, and from the standpoint of obtaining maximum operating efficiency it is highly desirable that the heat content of this liquid above inlet temperature be prevented as far as possible from being transferred to the incoming gaseous fluid before the latter reaches the compression chambers, in order to prevent temperature rise with consequent expansion of the gaseous fluid and with resultant decrease in volumetric capacity of the compressor. In another of its aspects, it is therefore a principal object of this invention to provide a novel form of compressor construction providing means whereby the transfer of heat from liquid within the compressor and heated by the heat of compression from being transferred from that liquid to incoming gas eous fluid flowing to the compression chambers and to thereby insure that the greatest possible mass of fluid is inducted int-o the chambers.

The manner in which this latter principal object and other and more detailed objects of this phase of the invention are attained will also be more fully elucidated as this specification proceeds.

For a better understanding of the more detailed nature and objects of the invention in its several aspects and of suitable apparatus for carrying the invention into effect, reference may now best be had to the ensuing portion of this specification, in which there is described by way of example but without limitation, different appropriate embodiments of apparatus for carrying the invention into effect, such description to be considered in conjunction with the accompanying drawings forming a part hereof, in which:

FIG. 1 is a longitudinal section of a compressor embodying the invention, taken on line 1-1 of FIG. 3;

FIG. 2 is a top plan view of the apparatus shown in FIG. 1;

FIG. 3 is a cross sectional view taken on line 33 of FIG. 1;

FIGS. 4 to 7 inclusive are fragmentary cross sectional views similar to FIG. 3, showing modifications of the structure shown in FIG. 3 and adapted to be incorporated in machines of the kind shown in FIGS. 1 and 2;

FIG. 8 is a fragmentary section taken on line 8-8 of FIG. 7;

FIG. 9 is a view similar to FIG. 1, partly in section and partly in elevation and with portions of the rotor structure broken away, of a further embodiment of the invention;

FIG. 10 is a cross section taken on line 1010 of FIG. 9; and

FIG. 11 is a view similar to FIG. 1, of the casing structure only of a further modification of the invention.

Referring now to the drawings, and more particularly to FIGS. 1 to 3 thereof, the compressor illustrated is of generally known construction and comprises a casing structure having a main barrel portion 10 closed at one end by a removable closure member 12 and providing a working space having intersecting co-planar bores 28 and 28' (FIG. 3). In the embodiment illustrated these bores are cylindrical, with parallel axes, and house helically threaded intermeshing male and female rotors of which the male rotor 14 is seen in FIG. 1, the rotors having been omitted from FIG. 3 for clarification. The barrel portion 10 of the casing has a low pressure port 16 located on one side of the plane of the axes of the rotors constituting what may be termed the low pressure side of the compressor and providing a radial inlet to the working space for the working fluid, and a high pressure port 18 on the opposite side of said plane constituting what may be termed the high-pressure side of the compressor and providing a radial-axial flow discharge of the compressed fluid, the direction of flow of the working fluid being indicated by the arrows 20 and 22 in FIG. 1. The terms male and female rotors as herein employed refer to the forms of rotors characteristic of this type of compressor, in which the pitch circle of the rotor lies at or adjacent to the bottom of the grooves in the rotor and the pitch circle of the female rotor is at or closely adjacent to the outer periphery of the rotor. In such compressors the intermeshing helical lands and grooves of the rotors form a series of chevron shaped compression chambers each composed of a portion of a male rotor groove and a portion of a female rotor groove, the base ends of the chambers being determined by the fixed transverse plane at the high pressure end of the working space and the apex ends of the chambers being formed by the places of intermesh between the coacting grooves. The latter move axially from the low pressure toward the high pressure end of the working space as the rotors revolve to reduce the volumes of the compression chambers. All of the foregoing structure is old and well-known in the art, as is its manner of functioning, and therefore need not be explained in greater detail herein.

In common with compressors of the type under consideration, the major portion of the inlet 16 lies to one side, in this case the upper side, of the plane of the rotor axes, while the major portion of the discharge port 18 is located at the opposite or lower side of said plane. With this arrangement the compression chambers are formed along the bottom portion of the rotors, the apex ends of the chambers traveling from right to left as viewed 4 in FIG. 1 with the rotors turning in the directions indicated by the arrows 34 and 34 in FIG. 3.

As previously noted the present invention is directed to wet or flooded type compressors and in the present embodiment liquid is supplied to the working space of the compressor through a series of longitudinally spaced supply openings 32 located along the line of intersection 28a of the bores on the lower or high pressure side of the working space.

The compression chambers are of course defined by the walls of the rotor grooves on the one hand and the confronting portions of the casing structure on the other hand and in order for these chambers to be effectively sealed a close running clearance must be maintained between the relatively moving parts. By way of example but without limitation, such clearance may advantageously be, in the case of a dry compressor, of the order of one-thousandth of an inch per inch of rotor diameter. In the case of a wet or flooded compressor, it may be less.

In the present embodiment of apparatus, the portions of the walls of the bores which provide running clearance between the casing structure and the rotors is substantially confined to the area corresponding to the area of each compression chamber when it is first formed by two groove portions coming into intermeshing relation at the low pressure end of the working space. The remaining portion of the walls of the bores is relieved to provide spacing in radial direction between the walls and the peripheries of the rotors, which spacing is many times greater than the spacing represented by the running clearances, and great enough to preclude any appreciable sealing effect between the relatively moving parts, even with liquid introduced into the working space. The spacing provided by such relieved portions may be of the order of A1, A or a larger fraction of an inch.

In the present embodiment the relieved and unrelieved portions of the barrel walls are separated by relatively abrupt shoulders 30 following helical lines which coincide respectively with the helix lines of the lands of the respective rotors. With this arrangement, the liquid, which has far greater viscosity than the gaseous working fluid, is confined in close running clearance space only over the minimum required area, with consequent reduction of churning losses to a minimum. The relieved portions of the walls of the barrel portion of the casing structure not only operate to minimize churning losses occasioned by the introduction of liquid into the working space, but also afford relatively open paths of communication over a large area between the inlet port proper and the grooves which are to be filled with the working fluid during the suction phase of the cycle. Thus in two different ways this feature of construction operates to improve overall efficiency.

During the compression phase of the cycle the gaseous fluid trapped in the compression chambers and being compressed therein, has two paths of egress or escape therefrom, one being through the running clearance between the rotors and the casing structure and the other being through the running clearance between the rotors along the line of intermesh therebetween.

In the case of a wet compressor the fluid escaping through these running clearances is a mixture of the gaseous fluid being compressed and of the sealing and cooling liquid that has been injected into the compression chambers. Since the compression process generates heat, the fluids leaking from the compression chambers are at a temperature higher than that of the fluid being drawn into the machine for compression, and by reference to FIG. 3, it will be seen that with the compression chambers being situated below the plane of the rotor axes and the low pressure zone of the working space being located above that plane, leakage from such chambers through the line of intermesh between the rotors is directed upwardly and in counter-current flow relation to the flow of the incoming working fluid. In the absence 5. of means to prevent it, this counter-current flow between relatively cool incoming gaseous fluid and relatively hot fluid escaping from the compression chambers, affords the maximum of heat transfer from the hot liquid to the incoming cool gas. This in turn results in maximum heating and expansion of the latter before it enters the grooves which subsequently form the compression chambers, with consequent reduction in volumetric capacity of the compressor.

In order to minimize this adverse effect, the present invention contemplates the provision of baflling means positioned to provide an obstruction preventing this adverse counter-current flow and to effect a kind of flow which will minimize the rate of heat exchange between the two bodies of fluid. To this end bafliing means is provided which in the present embodiment is in the form of a deflecting member disposed in radially spaced relation with respect to the peripheries of the rotors and extending longitudinally of the working space between the line of intermesh between the rotors, through which the leakage occurs, and the inlet through which the incoming supply of gaseous working fluid is flowing toward the rotors. In the embodiment of FIG. 3 this baflling means takes the form of a deflector member 36 having symmetrically curved laterally extending blade portions each operative to deflect the fluids leaking past the line of intermesh between the rotors and impinging upon the blades, laterally toward the relieved side walls of the casing structure. Such deflected flow results in a hot leakage liquid traversing the incoming gaseous fluid in a transverse flow relationship which results in the minimum of opportunity for heat exchange between the two media, with resultant minimum of preheating of the incoming gaseous fluid before compression takes place.

While the above described action alone is sufiicient to effect improvement in performance, the removal of escaped liquid from the apparatus show that it may be cooled before being returned thereto for sealing purposes through thefliquid feeding or injection orifices 32 may in many instances be desirable in order further to improve performance. To this endthere may advantageously be added means for such removal such as shown in the modification illustrated in FIG. 4. In accordance with this concept, the relieved portions of the walls, at the level where the walls are impinged by liquid deflected by the deflector member 36, are provided with longitudinally extending drainage troughs 37, which advantageously are arranged with a slight pitch causing the liquidcaught therein to flow toward one end of the working space, from which the liquid may be drained through a suitable drainage opening 46 in the end wall of the casing structure.

Other specific forms of apparatus may readily be employed to effect the deflection and drainage of hot leakage liquid, and one suitable form of modification is shown by way of example in FIG. 6. In this embodiment the blade portions of the deflector member 36 are curled inwardly at their outer edges to form troughs 38 into which the fluids impinging the deflective member are diverted and collected for drainage from the working space of the compressor through the drainage openings 46.

In FIG. 7 still another embodiment is illustrated in which a corrector member 42 is disposed between the deflector member 36 and the inlet opening. The deflected fluids pass between the inturned edges 40 of the deflected member at the overlying edges 44 of the collector member to accumulate in the trough formed by the deflector member itself and to drain through the opening 46.

It will be recalled that in addition to the leakage path afforded by the line of intermesh between the rotors, there is also the leakage path through the running clearances between the rotors and the casing structure. The latter leakage, if unimpeded, permits flow of hot liquid into the low pressure zone of the working space where it can give up at least some of its heat to the incoming gaseous fluid with consequent adverse results. To minimize this ill effect, the invention further contemplates the provision of baflle means which will minimize the flow of hot leakage fluid along the barrel walls from the unrelieved to i the relieved portions thereof and a suitable form of apparatus for effecting this purpose is illustrated in FIG. 5. As shown in this modification inwardly projecting fins 48 are provided extending inwardly from the relieved wall portions closely adjacent to the shoulders 30, these fins advantageously having substantially the same helix angle as the shoulders and the fins acting as dams for stopping and turning back hot liquid tending to flow upwardly along the walls of the working space in the low pressure zone, in heat exchange relation to the incoming gaseous fluid in that zone. The hot fluid thus intercepted by these fins is advantageously removed from the working chamber through suitably positioned drainage openings 50 appropriately located at the lower ends of these helically disposed fins.

All of the foregoing embodiments of apparatus have been described as incorporated in a casing structure providing for radial admission only of the incoming working fluid. The scope of the invention and the advantages to be derived from its use are, however, not restricted to this specific form of apparatus, but are equally applicable to compressors of the kind in which the admission of working fluid is through an axial rather than a radial inlet or through a combined axial-radial flow inlet similar to the axial-radial flow discharge shown in FIG. 1.

FIGS. 9 and 10 illustrate one suitable embodiment for incorporating the principles of the invention in a compressor having an axial flow inlet. In this construction the barrel portion 10 of the casing structure is provided wth a low pressure port 16 at one end thereof, the low pressure end closure member 12 being formed to provide an inlet passage for chamber 52 for working fluid in communication with port 16.

In this embodiment, as in the one shown in FIG. 1 the discharge port 18 is of the combined radial-axial flow type located at the lower side of the compressor, while the major portion of the inlet port is located above the plane of the rotor axes. In FIGS. 9 and 10 the female rotor 15 as well as the male rotor 14! appears and as will be evident from these figures, the reduction in churning losses is achieved by confining the area of close running clearances between the rotors and the walls of the bores of the casing structure to the area representing the maximum size of the compression chambers. This is done by relieving the walls of the barrels to provide the radially widely spaced portions 26, the relieved and unrelieved portions of the walls of the bores being separated along helical lines 30 one of which appears in FIG. 9. With the rotors turning in the direction indicated by the arrows in FIG. 10, it will be evident that fluids leaking from the compression chambers will be projected upwardly from the line of intermesh between the rotors to impinge against the upper relieved wall portion of the bores of the casing structure. This liquid, when restrained and deflected tends to flow axially along the relieved wall surface toward and into the inlet passage 52, due to the direction of the fluid flow from the intermesh between the rotors. In order to prevent this baflling means in the form of a radially inwardly projecting lip 54- is provided at the inlet end of the barrel portion of the casing, the radially inner face of this lip being located to provide only a close running clearance between itself and the inlet ends of the rotors. With the axial flow of the liquid thus obstructed by the baffle provided by the lip 54, the rate and extent of heat exchange between the hot liquid and the incoming-gaseous fluid is reduced with consequent improvement in performance.

In FIG. 11 there is shown the casing portion of an embodiment in which the principles of the invention are applied to a compressor having a combined radial-axial flow inlet. In this embodiment the radial flow portion of the inlet is indicated at lfia while the axial flow portion of the inlet is indicated at 16b. In order to prevent intermingling and heat exchange between hot liquid escaping through the line of intersection between the rotors and the incoming working fluid entering radially through the inlet portion 16a, the radial portion of the inlet is baffled by a deflector member 36 extending axially along the length of the radial portion of the ilet. As indicated in the drawing, this baflie may advantageously be of the kind illustrated in FIG. 3, but obviously may be of any of the other specific forms of construction illustrated in the previously described modifications. To prevent flow of hot liquid from the surface of this baffle or deflector and from other relieved wall portions of the bores, the easing structure is provided with an additional bafl le in the form of a lip 54 similar to that shown in FIG. 9.

While for the purposes of clarity and simplicity the modifications shown in FIGS. 9 and 11 omit illustration of baffling means such as the fins 48 shown in FIG. and the several drainage openings such as the openings 46 and 50 shown in FIGS. 5 to 8, it will be understood that all of these features of construction may readily be applied to the modifications of FIGS. 9 and 11 and also that the deflector 36 in the modifications shown in FIG. 11 may take any of the forms previously described.

While for purposes of illustration several different embodiments of appropriate apparatus have been illustrated and described herein by way of example, it is to be understood that the invention is in no way limited to such constructions but is to be understood as embracing all forms of apparatus falling within a scope of the appended claims.

We claim:

1. A rotary piston, positive displacement compressor having a housing structure including a barrel portion comprised of intersecting bores with co-planar axes providing a working space extending longitudinally of said barrel portion, such structure having a low pressure port communicating with one end of said space to provide an inlet a major portion of which is located at one side of the plane of said axes constituting the low-pressure side of the compressor and a high pressure port spaced from said low pressure port to provide a discharge from said space the major portion of which is located at the opposite side of said plane constituting the high-pressure side of the compressor, rotors provided with helical lands and grooves having an effective wrap angle of less than 360 degrees rotatably mounted in said bores and comprising a male rotor having lands provided with convexly curved flanks and intervening grooves the major portions of which lie outside the pitch circle of the male rotor and a female rotor having lands provided with concavely curved flanks and intervening grooves the major portions of which lie inside the pitch circle of the female rotor, the lands and the grooves of said rotors intermeshing to form with the confronting portions of said housing structure chevron-shaped compression chambers each comprised of communicating portions of a male rotor groove and a female rotor groove, said chambers being defined at their base ends by an axially fixed transverse plane at which said high pressure port is located and at their apex ends by the lands of the rotors coming into mesh at the low pressure ends thereof to provide places of intermesh traveling axially toward said transverse plane as the rotors revolve to decrease the volumes of the chambers, the Walls of those portions of said bores constituted by the said confronting portions of said housing structure being radially spaced from the crests of the lands of the respective rotors to provide close running clearances between the relatively movable parts capable of being closed by a film of sealing liquid, substantially all of the remaining portions of the walls of said bores being relieved to provide spacing between the relieved part of said remaining portions and the crests of said rotors, said spacing having a radial extent many times that of said 8 running clearances and sufficiently great to preclude any sealing effect between the rotors and the relieved part of the walls and means for supplying liquid to said compressor for sealing said running clearances and cooling the contents of said chambers.

2. A compressor as defined in claim 1 in which the portion of the housing having running clearance with respect to the peripheries of the rotors is of generally triangular form substantially conforming to the perimeter of said chambers when the apex ends thereof are at the inlet end of the compressor.

3. A compressor as defined in claim 2 in which the side edges of said triangular portion are helices having substantially the same helix angles as the helical crests of the lands of the respectively confronting rotors.

4. A compressor as defined in claim 3 in which each of said side edges is defined by a relatively abrupt shoulder between the portion of the barrel wall providing run ning clearance and the relieved portion thereof providing said spacing.

5. A rotary piston, positive displacement compressor having a housing structure including a barrel portion comprised of intersecting bores with co-planar axes providing a working space extending longitudinally of said barrel portion, such structure having a low pressure port communicating with one end of said space to provide an inlet a major portion of which is located at one side of the plane of said axes constituting the low pressure side of the compressor and a high pressure port spaced from said low pressure port to provide a discharge from said space the major portion of which is located at the opposite side of said plane constituting the high pressure side of the compressor, rotors provided with helical lands and grooves having an effective wrap angle of less than 360 rotatably mounted in said bores and comprising a male rotor having lands provided with convexly curved flanks and intervening grooves the major portions of which lie outside the pitch circle of the male rotor and a female rotor having lands provided with concavely curved flanks and intervening grooves the major portions of which lie inside the pitch circle of the female rotor, the lands and the grooves of said rotors intermeshing to form with the confronting portions of said housing structure chevron-shaped compression chambers each comprised of communicating portions of a male rotor groove and a female rotor groove, said chambers being defined at their base ends by an axially fixed transverse plane at which said high pressure port is located and at their apex ends by the lands of the rotors coming into mesh at the low pressure ends thereof to provide places of intermesh traveling axially toward said transverse plane as the rotors revolve to decrease the volumes of the chambers, the walls of those portions of said housing structure being radially spaced from the crests of the lands of the respective rotors to provide close running clearances between the relatively movable parts capable of being closed by a film of sealing liquid, a substantial part of the remaining portions of the walls of said bores on the low pressure side of the compressor being relieved to provide spacing in open communication with said low pressure port between the relieved portions and the crests of said rotors, said spacing having a radial extent many times that of said running clearances and sufficiently great to preclude any sealing effect between the rotors and the relieved part of the walls, means for supplying liquid to said compressor for sealing said running clearances and cooling the contents of said chambers, and baflle means in said relieved portion of the barrel wall for intercepting liquid escaping through said running clearance from the compression chambers to the low pressure side of said working space.

6. A compressor as defined in claim 5 in which said batlle means is in the form of internally projecting helical fins each located adjacent to and following the helix line of one of said shoulders.

7. A compressor as defined in claim 6 in which openings are provided for drainage from said working space of liquid intercepted by said fins.

8. A compressor as defined in claim including baflle means located to provide an obstruction preventing direct flow to said inlet of liquid escaping from said compression chambers to the low pressure side of the compressor along the line of intermesh between the rotors.

9. A compressor as defined in claim 8 in which said low pressure port provides for radial admission of working fluid through the barrel portion of said casing structure and in which said baflie means comprises a deflector member extending longitudinally of said casing structure in radially spaced relation to said rotors, said deflector member being disposed between said line of intermesh and said low pressure inlet and being shaped to deflect fluids impinging thereon laterally toward relieved portions of the walls of said barrel portions adjacent to said low pressure inlet.

10. A compressor as defined in claim 9 in which said deflector member is symmetrical with respect to said line of intermesh and comprises curved blade portions conforming substantially to the curvature of the circumferences of the rotors.

11. A compressor as defined in claim 9 in which the radial spacing between the rotors and said deflector member is suflicient to preclude any appreciable sealing effect between the confronting members.

12. A compressor as defined in claim 9 in which the longitudinal extent of said deflector member is substantially coextensive with the longitudinal extent of said low pressure port.

13. A compressor as defined in claim 9 in which the relieved wall portions toward which liquid is deflected are provided with drainage means for catching and conducting deflected liquid away from said low pressure inlet.

14. A compressor as defined in claim 13 in which said drainage means comprises longitudinally extending troughs.

15. A compressor as defined in claim 14 in which said troughs are pitched to create drainage flow of the collected liquid and drainage openings are provided for discharge of said liquid from the working space of the compressor.

16. A compressor as defined in claim in which the laterally outer edges of said blade portions are inwardly bent to provide troughs for catching and conducting deflected liquid away from said low pressure inlet.

17. A compressor as defined in claim 16 in which drainage openings are provided in communication with said troughs for discharge of collected liquid from the working space of the compressor.

18. A compressor as defined in claim 10 in which a collecting member interposed between said deflecting member and said low pressure inlet cooperates with the former to provide a canal for draining the collected liquid away from the latter.

19. A compressor as defined in claim 18 in which an opening is provided for drain-age of liquid from said canal to the exterior of said casing structure.

20. A compressor as defined in claim 5 in which said low pressure inlet provides for axial admission of working fiuid to said working space and said baflle means comprises a lip extending radially inwardly from the relieved portions of said bores at the inlet ends thereof which communicate with said low pressure inlet, said lip providing only a running clearance between itself and the inlet ends of said rotors to thereby restrict and substantially prevent free axial flow of liquid from the inlet ends of the walls of the relieved portions of said bores into the inlet passage leading to said low pressure inlet.

21. A compressor as defined in claim 6 in which said low pressure inlet further provides for axial admission of working fluid to said working space and said bafl le means further comprises a lip extending radially inwardly from the relieved portions of said bores at the inlet ends thereof which communicate with said low pressure inlet, said lip providing only a running clearance between itself and the inlet ends of said rotors to thereby restrict and substantially prevent free axial flow of liquid from the inlet end of said deflector member and from the inlet ends of the walls of the relieved portions of said bores into the inlet passage leading to said low pressure inlet.

References Cited by the Examiner UNITED STATES PATENTS 1,319,776 10/1919 Kerr 230-143 1,409,868 3/1922 Kien 230-143 1,424,312 8/1922 Leonard 230-141 1,439,628 12/1922 Kien 230-205 1,672,571 6/1928 Leonard 230-205 1,673,260 6/1928 Meston et al. 230-205 1,675,524 7/1928 Zaj-ac 230-205 2,111,568 3/1938 Lysholm et al. 230-143 2,425,000 8/1947 Paget 230-143 2,474,653 6/1949 Boestad 230-143 2,477,002 7/1949 Paget 230-143 2,477,004 7/1949 Paget 230-143 2,642,003 6/1953 Whitfield 103-128 2,652,192 9/1953 Chilton 230-143 2,755,990 7/1956 Nilsson et al. 230-143 2,804,260 8/1957 Nilsson ct al. 230-143 2,849,988 9/1958 Nilsson 230-143 2,963,884 12/1960 Rosenschold et al. 230-143 3,073,514 1/1963 Bailey et al. 230-143 3,086,474 4/1963 Sennet 103-128 FOREIGN PATENTS 220,581 5/1957 Australia. 832,386 4/1960 Great Britain.

DONLEY J. STOCKING, Primary Examiner. 

1. A ROTARY PISTON, POSITIVE DISPLACEMENT COMPRESSOR HAVING A HOUSING STRUCTURE INCLUDIDNG A BARREL PORTION COMPRISED OF INTERSECTNG BORES WITH CO-PLANAR AXES PROVIDING A WORKING SPACE EXTENDING LONGITUDINALLY OF SAID BARREL PORTION, SUCH STRUCTURE HAVING A LOW PRESSURE PORT COMMUNICATING WITH ONE END OF SAID SPACE TO PROVIDE AN INLET A MAJOR PORTION OF WHICH IS LOCATED AT ONE SIDE OF THE PLANE OF SAID AXES CONSTITUTING THE LOW-PRESSURE SIDE OF THE COMPRESSOR AND A HIGH PRESSURE PORT SPACED FROM SAID LOW PRESSURE PORT TO PROVIDE A DISCHARGE FROM SAID SPACE THE MAJOR PORTION OF WHICH IS LOCATED AT THE OPPOSITE SIDE OF SAID PLANE CONSTITUTING THE HIGH-PRESSURE SIDE OF THE COMPRESSOR, ROTORS PROVIDED WITH HELICAL LANDS AND GROOVES HAVING AN EFFECTIVE WRAP ANGLE OF LESS THAN 360 DEGREES ROTATABLY MOUNTED IN SAID BORES AND COMPRISING A MALE ROTOR HAVING LANDS PROVIDED WITH CONVEXLY CURVED FLANKS AND INTERVENING GROOVES THE MAJOR PORTIONS OF WHICH LIE OUTSIDE THE PITCH CIRCLE OF THE MALE ROTOR AND A FEMALE ROTOR HAVING LANDS PROVIDED WITH CONCAVELY CURVED FLANKS AND INTERVENING GROOVES THE MAJOR PORTINS OF WHICH LIE INSIDE THE PITCH CIRCLE OF THE FEMALE ROTOR, THE LANDS AND THE GROOVES OF SAID ROTORS INTERMESHING TO FORM WITH THE CONFRONTING PORTIONS OF SAID HOUSING STRUCTURE CHEVRON-SHAPED COMPRESSION CHAMBERS EACH COMPRISED OF COMMUNICATING PORTIONS OF A MALE ROTOT GROOVE AND A FEMALE ROTOR GROOVE, SAID CHAMBERS BEING DEFINED AT THEIR BASE ENDS BY AN AXIALLY FIXED TRANSVERSE PLANE AT WHICH SAID HIGH PRESSURE PORT IS LOCATED AND AT THEIR APEX ENDS BY THE LANDS OF THE ROTORS COMING INTO MESH AT THE LOW PRESSURE ENDS THEREOF TO PROVIDE PLACES OF INTERMESH TRAVELING AXIALLY TOWARD SAID TRANSVERSE PLANE AS THE ROTORS REVOLVE TO DECREASE THE VOLUMES OF THE CHAMBERS, THE WALLS OF THOSE PORTIONS OF SAID BORES CONSTITUTED BY THE SAID CONFRONTING PORTIONS OF SAID HOUSING STRUCTURE BEING RADIALLY SPACED FROM THE CRESTS OF THE LANDS OF THE RESPECTIVE ROTORS TO PROVIDE CLOSE RUNNING CLEARANCES BETWEEN THE RELATIVELY MOVABLE PARTS CAPABLE OF BEING CLOSED BY A FILM OF SEALING LIQUID, SUBSTNATIALLY ALL OF THE REMAINING PORTIONS OF THE WALLS OF SAID BORES BEING RELIEVED TO PROVIDE SPACING BETWEEN THE RELIEVED PART OF SAID REMAINING PORTIONS AND THE CRESTS OF SAID ROTORS, SAID SPACING HAVING A RADIAL EXTENT MANY TIMES THAT OF SAID RUNNING CLEARANCES AND SUFFICIENTLY GREAT TO PRECLUDE ANY SEALING EFFECT BETWEEN THE ROTORS AND THE RELIEVED PART OF THE WALLS AND MEANS FOR SUPPLYING LIQUID TO SAID COMPRESSOR FOR SEALING SAID RUNNING CLEARANCES AND COOLING THE CONTENTS OF SAID CHAMBERS. 